Urethane may be formulated into almost every known type adhesive. Contact adhesives, pressure-sensitive adhesives, two-component thermosetting adhesives and thermoplastic adhesives. Urethanes are generally not suitable for joining materials such as rigid metals, but are useful as adhesives where two unlike materials are to be joined. Thermoplastic polyurethanes are particularly suited for use where the joined materials are to be subjected to much flexure, and in applications requiring elongation to allow for difference in expansion and contraction. A general discussion of the use of urethanes as adhesives can be found in, for example, the publication by E. N. Doyle, "The Development and Use of Polyurethane Products," McGraw-Hill Book Company, (1971), pp. 212-224. A problem with thermoplastic polyurethane is that often times sufficient bond for particular applications cannot be effected. Thermoplastic polyurethane adhesives also tend to exhibit levels of water sensitivity that are unacceptable for various applications.
U.S. Pat. No. 3,377,303 discloses a specific group of polymeric fat acid polyamides which possess properties suitable for hot melt adhesive applications. A piperazine type product includes a copolymerizing acid and amine. A dipiperidyl type product is suitable with either a copolymerizing acid or amine with a polymeric fat acid, as well as with compositions which include a dimer diamine and dicarboxylic acid other than a polymeric fat acid. The polyamides disclosed in this patent are described as being suitable for bonding vinyl based polymer substrates. A problem with the polyamides described in this patent is that they tend to exhibit levels of water sensitivity that are not suitable for certain applications. Departing now from the teachings of this patent the applicant has discovered that polyamides of the type described in this patent can be combined with certain thermoplastic polyurethanes to produce adhesive materials that exhibit, among other things, excellent water sensitivity characteristics.
Thermoplastic polyesters such as polyethylene terephthalate and polybutylene terephthalate are produced by the polyesterification reaction between a single glycol and a single di-basic acid. Copolyesters are those polyesters whose synthesis uses more than one glycol and/or more than one di-basic acid. A copolyester chain is less regular than the monopolyester chain and therefore has a reduced tendency to crystallize. Some of the copolyesters, as a result, normally are amorphous, some are normally crystalline, and some can be made to be either crystalline or amorphous, depending upon the processing conditions. Thermoplastic copolyesters are prepared and processed in much the same manner as the thermoplastic monopolyesters. Of particular significance is a polymer of cyclohexane dimethanol and terephthalic acid with another acid substituted for a portion of the terephthalic acid that otherwise would have been required. U.S. Pat. No. 3,372,148 discloses the preparation of a terephthalic acid-aliphatic acid copolyester which is indicated to be useful as an adhesive. The copolyester disclosed in this patent is made from ethylene glycol, neopentyl glycol, terephthalic acid and an aliphatic dicarboxylic acid.
Polyester-polyamides are known. For example, U.S. Pat. No. 2,852,492 discloses the preparation of N,N'-bis-(p-carboalkoxybenzoyl) piperazines which are indicated to be useful in the manufacture of linear polyesters containing chain amide groups. This patent indicates that the quenchability of well known polyester compositions, particularly those prepared by condensing a glycol with an aromatic dicarboxylic acid, can be improved by forming a copolyester of such reactants with the compounds described in this patent. U.S. Pat. No. 2,954,364 discloses the preparation of polyester-polyamides by heating ethylene glycol with a compound selected from the group consisting of N,N'di-(5-carboxypentyl) oxamide, N,N'-di-(6-carboxyhexyl) oxamide, and their methyl or beta-hydroxyethyl esters. This patent indicates that the polyester-polyamides so formed can be processed by conventional means into fibers, films and injection moldings.